1. Field of the Invention
The present invention relates to an indexing rotary actuator which is preferably used in industry for automation of rotary motion of indexing conveyors and rotary indexers.
2. Description of the Background Art
Fluid or air-powered rotary actuators are commonly used in industry for automation of rotary motion. Four conventional rotary actuator types include a vane type, a piston type with rack and pinion, a piston type with a lever actuated shaft, and a piston type with a chain and sprocket. Vane type actuators use fluid power to force a vane, which is fastened to an output shaft, to rotate through an arc less than 360.degree.. The output shaft of the vane type rotary actuator must reciprocate to be reset to the start position.
The piston type rotary actuator with rack and pinion utilizes linear double acting piston motion to actuate the rack and pinion mechanism wherein the output shaft is fastened to the pinion. Angular displacement generally up to 360.degree. may be achieved. Reciprocation is necessary to reset the rotary actuator shaft to the start position. The piston type rotary actuator with lever activated shaft utilizes linear piston motion to actuate the lever mechanism which rotates the output shaft. Angular displacements are usually 180.degree. or less. Reciprocation is necessary to reset the rotary actuator to the start position. The piston type rotary actuator with chain and sprocket utilizes linear piston motion to actuate the chain and sprocket mechanism, wherein the output shaft is fastened to the sprocket. This type of rotary actuator provides angular displacements up to five full revolutions. Reciprocation is necessary to reset the rotary actuator to the start position.
A variation of the piston type rotary actuator with rack and pinion as described above uses a pawl and ratchet mechanism together with roller bearing/cam clutches, which transmit torque in one direction and which run freely in the reverse direction. This permits the rack and pinion to drive the output shaft through a fixed angular displacement in the same direction each time the unit is cycled. While the linear piston completes a full return stroke, the output shaft remains stationary due to the roller bearing/cam clutch. Available angular displacements are limited to simple fractions of a whole revolution, from about 30.degree. to 360.degree. per step.
All of the above mentioned rotary actuators, with the exception of the piston-type rotary actuator with rack and pinion variation described above, require additional mechanical elements such as pawls and ratchets to attain positional accuracy necessary for complete rotary and linear indexing. Consequently, the requirement of additional mechanical elements increases manufacturing costs of the conventional rotary actuators. Furthermore, the pawls and ratchets are subject to mechanical wear which decreases accuracy of indexing and which eventually results in system failure. In the piston type rotary actuator with rack and pinion variation described above, the additional mechanical elements are disposed internally within the rotary indexer. System repair is difficult and costly.
A further disadvantage of conventional rotary actuators as described above is energy inefficiency. The conventional systems require that the main motive source, either the vane or piston, completes a full return stroke during which no work is done. Accordingly, the conventional rotary actuators are 50% efficient at best.